The Asus board is for a different series of AMD processors. So, the Asrock is the only one of those two you can use.
The Asrock has a AM3+ socket, so it can use newer FX processors should you decide to upgrade in the future. But it is limited to 95W processors. If you don't see yourself ever upgrading beyond that, it will be fine.
If you think you might want to get a faster processor in the future and require a mATX size board, this would be the ideal choice: http://www.asrock.com/mb/AMD/970M%20Pro3/
And it is in that same price range:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157582